1. Field of the Invention
The present invention relates to water-blown polyurethane foams which have been modified by incorporation of specific zeolties in order to improve the combustion resistance of the polyurethane foam.
2. Prior Art
The principal commercial procedure for the production of urethane foams is the technique of simultaneous reaction of polyol, polyisocyanate, water, catalyst, surfactant and various foaming aids. In addition to the expected urethane forming reaction between polyol and isocyanate, water reacts with another isocyanate to release carbon dioxide and form amine. The amine reacts with another diisocyanate to form urea groups. This complex set of reactions yields a urea-urethane polymer which is highly diluted during the foaming reaction by evolved carbon dioxide and possibly by the addition of halocarbons or other volatilizable compounds termed blowing agents. The foam which results is termed a water-blown foam.
These urethane foams have many uses such as packaging and insulation. Significant commercial volumes are employed for applications such as mattresses, furniture, automobile seating and carpet underlayment. In these latter applications, the load bearing capability of the foam is very important. To yield increased load bearing, fillers are employed in the systems. Highly effective among these fillers are organic fillers such as those prepared by polymerizing acrylonitrile or copolymerizing acrylonitrile and styrene in a polyol, termed polymer polyol. When a polymer polyol is converted into water-blown, urethane foam, a highly complex chemical and physical structure results. This foam, used in mattresses, furniture, automobile seating and carpet underlayment, is an open-celled foam of ambient air, the solid phase of which is a crosslinked network of polyurea-urethane blocked polymer, the linkages of which are separated by long, flexible elastomeric chains derived from base polyol used in the formulation and from which the polymer polyol was made. The elastic network is reinforced by the dispersed polymer filler. The characteristics of these water-blown urethane foams have led to their wide commercial acceptance. Among these special characteristics are their uniformity, load-bearing capability and resiliency. The key to successful manufacture of such complex polymeric structures is control of the reactivity and sequence of reactions which take place particularly when manufacturing engineered, shaped products such as molded foams or very large pieces of foam with controlled physical or engineering properties such as slab foams. For a detailed description of these processes, a number of texts or handbooks can be consulted such as Polyurethane Handbook, Edited by G. Oertel, Hanser Publishers, Munich and New York (1985).
An alternative approach to organic fillers is the incorporation of inorganic fillers into polyurethane foams for increasing foam modulus and density. Among the many types of inorganic fillers discussed in the art is zeolites. Zeolites have reportedly been incorporated in rigid foams for several purposes, including formulations which have combustion resistance. Exemplary of the uses of zeolites in foams are: as carriers for flame retardant additives, as carriers for foam reaction catalysts, and as carriers for halocarbon blowing agents. Zeolites have been incorporated into rigid foam formulations to absorb traces of water, inadvertently present in rigid formulations, which would lead to lowered thermal insulation capability of the foams produced. Finally, zeolites have also been incorporated into packaging foams for their desiccant properties. The following references are illustrative of this art:
U.S. Pat. No. 4,526,906, concerns microcellular polyurethane and teaches use of fire retardants in combination with zeolites. The patent specifically notes that the zeolites are not useful without the addition of flame retardants.
U.S. Pat. No. 4,518,718, concerns rigid foams with desiccant properties which can be used in packaging and storage containment of instruments or electronic parts and the like.
U.S. Pat. No. 4,447,565, incorporates zeolites in a thermosetting foam for many of the same purposes as cited in the '718 patent.
"Ken-React Reference Manual", 1987, Kenrich Petrochemicals, Inc. Bayonne, N.J., "Synergistic Dispersion Effects in Zeolite Performance" describes use of organo-titanates to improve the effectiveness of Molecular Sieves in rigid polyurethane foam formulations. The zeolites are used to absorb traces of moisture which would react with isocyanate to produce carbon dioxide during the manufacture of closed cell, rigid urethane insulating foam and thereby reduce the K-factor and K-factor stability of the thermal insulating foam.
U.S. Pat. No. 4,539,049, concerns organo-zirconates useful in the same way as the products described immediately above.
U.S. Pat. No. 4,288,559, concerns impregnating preformed urethane foams with a dispersion latex containing surfactants, aluminum trihydrate and zeolite.
West German Patent DE 35 3671, concerns impregnating foam with a natural rubber or chloroprene latex which contains magnesium oxide or zinc oxide sufficient to neutralize any carboxylic acids stabilizing the latex and ca. 20 percent by weight aluminum trihydrate.
U.S. Pat. No. 3,326,844, concerns bubble-free polyurethane coatings containing zeolites such as Molecular Sieve 4A.
Japanese Patent Number 57/51728, concerns closed cell, rigid thermal insulating foam made by absorbing at least part of the blowing agent, e.g. a fluorocarbon, in a zeolite.
Japanese Patent Number 57/49628, concerns rigid foams with low thermal conductivity containing about 15 percent of zeolite.
Japanese Patent Number 56/41233, concerns use of zeolites as absorbants for gaseous blowing agents in making closed cell insulating foam.
Japanese Patent Number 54/39857, concerns blending clay mineral having combined water, evolvable at high temperature, and a boric acid or silicic acid salt in a urethane foam formulation to give fire-resistant thermal insulating foam. The mineral can be a zeolite and the salt can be sodium metaborate.
Japanese Patent Number 52/63997, concerns making foams from polyether triol-TDI prepolymer. 100 parts of the prepolymer and 20 parts water and 3 parts of zeolite produced a foam which was softer than if the zeolite had been omitted.
German Patent DE 1804362, concerns use of a sodium aluminosilicate zeolite together with MDI, CF3 blowing agent and catalysts and polyether to form cellular structures with compact surfaces and densities in the range of 6 lb/cu.ft.
Because of the wide use of urethane foams in home and commercial furnishings as well as in transportation, there has been an increasing emphasis on the health and safety aspects of this usage. Of particular concern has been ignition sensitivity and combustibility resistance of these products. These combustibility issues have been met by incorporation of fire retardants into the foams. These fire retardant additives are principally halogen/phosphorus containing compounds, often chlorinated or brominated phosphorus esters. While these additives have served their purposes well, there is growing concern over increased levels of smoke generation, rather than actual flaming, and the safety aspects of pyrolysis products which are at least noxious and often potentially toxic.
Accordingly, there has been a recognized need for a superior way of providing fire retardancy, i.e. advanced combustion resistance. This need is evident in the stringent requirements currently a part of various countries' fire codes, as well as established test procedures.